Cold weather adversely affects the starting of internal combustion engines, most particularly diesel engines, for several temperature related reasons. Inasmuch as diesel engines heat the fuel/air mixture by compression, it becomes increasingly difficult to achieve ignition temperature as ambient temperatures fall and diesel fuel will gel at any temperature much below 0 degrees F. Lubricating oils and diesel fuels also become more viscous at lower temperatures. There is a range of variation with compounding, but 15W40 motor oil for instance, becomes semi-solid at -20 degrees F., and 10W30 at -35 degrees F. As oil viscosity becomes greater it begins to impede, rather than lubricate, the movement of parts, especially of the pistons. Add to these factors an electric starting system having diminished output at low temperatures, and it will be appreciated that a diesel engine can become virtually unstartable when temperatures fall much below freezing.
A need for some viable engine preheating means has been recognized for many years, as evidenced by prior efforts to make such a system, but none have enjoyed any notable acceptance in the market. These devices include the examples shown in U.S. Pat. Nos. 2,616,412; 4,010,895 and 4,520,769.
The common cold weather practice has been to leave a diesel engine running at idle, even for extended periods, rather than to risk the effort of restarting. A good argument has been made that this is more economical and less stressful to an engine, but environmental awareness is causing a reevaluation of the practice. Certainly, a great quantity of fuel is burned, and the products of combustion released into the atmosphere, for the sole purpose of coping with this cold starting problem.
The Environmental Protective Agency is expected to address this practice on a national basis in pending "Clean Air" legislation, requiring that it be severely restricted or eliminated altogether. Already we have the advent of local legislation, such as in Denver, Colorado, where operators are limited to running the engines of parked vehicles for only 15 minutes of each hour.
There is a clear need for a practical, environmentally acceptable, engine heating system to maintain or restore operating temperatures in a completely safe and economical manner. To be both functional and acceptable for general use this system is must:
1. Be efficient;
2. Be capable of continuous, independent operation;
3. Operate in extreme conditions of cold and wind;
4. Warm the engine fuel as well as coolant; and
5. Be safe.
It is the object of the present invention to fulfill each of these requirements. Propane, or liquid natural gas (LNG) fired heating systems are well-known to the art, are inherently self-sufficient and have been proven to be safe and reliable. Gasoline fired systems are also quite feasible for this application but, on the basis of safety related considerations, a propane (LNG) fired system is considered to be somewhat better suited.
Efficiency includes, but goes well beyond operating cost, since a compact size is needed in order to have an acceptable cowl mounted unit. Moreover, this unit must be capable of heating an engine of 400 HP or more without reaching unsafe external temperatures. The required thermal efficiency is achieved in the present invention by passing the coolant heat exchange means through a fire-box held at temperatures in excess of 900 degrees F. Such temperatures serve to concentrate the potential for rapid heat exchange in a relatively small unit. This function is facilitated by radiant heat from an incandescent refractor fire-box lining which, along with direct flame exposure, involves the full surface area of the coolant heat exchanger. Refractory materials in general reach red incandescence as temperature increases to 900 degrees F., progressing through cherry red at 1,200 degrees and orange at 1,300 degrees, to a white range at 1,550 degrees and above, becoming a brilliant white at 1,750 degrees. The present invention functions anywhere in this range, but has proven more efficient at the higher temperatures.
The refractory lining properties are critical to proper functioning of this unit. This material must reach an incandescent red or white hot condition quickly with a relatively low heat input, and also provide thermal insulation so that conduction losses from the fire-box are minimized. There is no risk of heat exchanger burnout, even with a fire-box temperature of 1,750 degrees F., so long as care is taken to assure unrestricted coolant flow through the heating unit and back to the engine. It is also essential to avoid a steam trap by having the coolant outlet of the heating unit positioned at a lower elevation than the coolant inlet connection to the engine. Operation at these elevated temperatures allows fire-box size to be reduced accordingly and is considered to be a significant aspect of the invention.
The combustion gases pass down from the fire-box to a lower section where they are partially cooled while preheating incoming coolant. These gases are then passed over the propane (LNG) tank where the remaining heat helps to maintain supply pressure. Means for heating fuel are included in the heating unit. Air circulating through an outer jacket serves both to cool external surfaces and to provide a source for cab heat if it is desired.
The engine radiator provides an abundant excess of cooling capacity when the engine thermostat opens, and thus gives inherent protection from overheating should the heating unit output be excessive. A test unit, using a flame set so that the thermostat opened only slightly, has kept a 400 HP engine warm for as long as 18 hours, in -7 degree F. ambient conditions, while burning one 21/2 gallon propane tank, and better performance is anticipated of later models. This same test unit has performed well at altitudes of 10,500 feet and in 40 mph blizzards.